Quattro(A Beano Beater??)
By Miles Kingsbury

 
CAD Picture Quattro Initial Design

I have had a very enjoyable season racing my Bubble & Squeak faired trike but the winter is nearly upon us so it’s time to start thinking about a 2010 machine. I could of course use the same trike for the 2010 season but I do love designing and building but more importantly I am desperate to beat Slash.

FUNDERMENTALS
Firstly I would like to recommend two books that have helped me a great deal.

1. The Leading Edge by Goro Tamai which is mainly about solar cars.
2. The World’s Most Fuel Efficient Vehicle by various authors which is about designing and building a fuel cell car.

Before going into details of a new design let’s get the maths out of the way first.

Most of our HPV circuit races are won (by Slash) with an average speed of about 35mph (15.5m/s).

If I want to beat the little s###, I will have to go a little faster or saw up his Beano!

The power required to maintain 35mph is made up of two main elements.

Air Resistance Power = CdxA x½ρV³

Where Cd is the drag coefficient, A is the frontal area in m², ρ is air density (1.2kg/m³ at 20°C) and V is the speed in m/s.

Rolling Resistance Power =CrxVxN

Where Cr is the rolling resistance coefficient, V is the speed in m/s and N is the normal force in Newtons (kgx9.81) on the tyre.

There are other mechanical losses such as bearings and chain friction but these are small and I will ignore them in the following examples.
35mph Beano Power

The Cd for the Beano is probably about 0.12 taking into account gaps, wheels etc. The frontal area is about 0.35m².

Air Resistance Power = CdxA x½ρV³ gives 0.12x0.35x0.5x1.2x15.5³ =94W

The Cr is about 0.006 for good cycle tyres, Slash weighs about 65kg and the Beano about 17kg giving a total weight of 82kg.

Rolling Resistance Power =CrxVxN gives 0.006x15.5x82x9.81 =75W

Therefore Slash needs to put out about 169W to maintain 35mph in the Beano. So why is he so sweaty when he gets out after a race?
This is because it is his cruising power and doesn’t take into account accelerating out of corners and climbing hills.

35mph Quattro Power
The frontal area of Quattro is about 0.6m². Let us hope to get the drag coefficient down to the same value of the Beano at 0.12.

Air Resistance Power = CdxA x½ρV³ gives 0.12x0.6x0.5x1.2x15.5³ =160W

Let’s show Mike Burrows some respect and assume the smaller wheels have a slightly higher Cr of about 0.0065, I weigh about 73kg and guess the

Quattro will weigh about 20kg giving a total weight of 93kg.

Rolling Resistance Power =CrxVxN gives 0.0065x15.5x93x9.81 =92W

This makes a total of 252W which is an attainable figure but does give us an idea of what we are up against.
35mph “Upright” Racing Bike

Putting things in to perspective, a racing cyclist in a crouch position has a frontal area of about 0.3m² and a Cd of 0.9.

Rolling Resistance Power =CrxVxN gives 0.006x15.5x82x9.81 =75W

Air Resistance Power = CdxA x½ρV³ gives 0.9x0.3x0.5x1.2x15.5³ =603W

This makes a whopping 678W!  I could probably get a Knighthood if I was able to generate this sort of power output.

New Design
Bubble & Squeak is great fun to drive and is quite competitive, particularly on twisty circuits. I can throw it round corners with gay abandon and if I get it wrong I can just jam on the brakes or take to the grass. However it does have a few faults.

Ground Clearance
With only 25mm of ground clearance and a flat floor, the Trike bottoms out on all but the smoothest circuits, I have also worn away the heels of my expensive Sidi cycling shoes.

So when we went to the world championships in Holland this year, I didn’t take the trike as I could have only competed in three of the six events because of rough and uneven surfaces.

A ground clearance of 75mm to cope with speed bumps would be lovely.

Turning Circle
Curborough was a nightmare for me this year. After quite a bit of filing and sanding I was still unable to get round the hairpin without severe rubbing of the front tyres. The poor turning circle also makes general manoeuvring tiresome.

 A turning circle diameter of about 7m would allow me to turn in most roads.

Weight
B&S weighs about 27kg which is less than a Quest but still too much compared with most other recumbents. My sprint results this season have shown that I am carrying too much weight, not to mention the dreaded Hog Hill.

A total weight of less than 20kg should be achievable.

Cooling/Ventilation
The combination of a large bubble screen and poor internal ventilation make B&S very hot, particularly on sunny days. I found that my performance dropped off dramatically after 25-30mins at most races this year. The screen also fogged at some of the events.

Direct ventilation onto my face and screen would help considerably.

Initial Specification
 

SOLUTIONS
My idea of going for four wheels is mainly because I want to try something different rather than going for a Quest type layout. The Quest is a very well sorted all rounder and is hard to beat on practicality and performance.

When I started thinking about the design, I wasn’t planning to compete in pedal car races. Their regulations had a length restriction of 2030mm which was too short for my design; this has now been increased to 3000mm.

The main advantage I can see with a four wheeler is maintaining the cornering stability of B&S with the extra ground clearance I would like to achieve. After all, how many three wheel cars do you see on the roads?

Four wheel steering gives a better turning circle for the same amount of wheel movement and maybe less scrubbing round the corners, but whether it is worth the extra complexity will have to be seen.

I have decided to go for 16” wheels for a number of reasons. There is now a good selection of tyres for this size, they are smaller and easier to package in particular when steering and they are lighter. I estimate a total weight saving of over 1kg on 5 wheels (including spare).

All four wheels will be the same with a plain hub. The bearings and brakes will stay with the chassis, which should keep the weight down and make it possible to carry a spare.

The wheels are leaning in at 80 to give maximum track width with minimum frontal area. I have based this angle on the research that was done for the PACII fuel efficiency car. They suggest that angles up to 80 have a very small rolling resistance penalty.

The leaning wheels have made it difficult to get the front drive sorted. I have toyed with various ideas including a lay shaft with short chains and universal joints.

The screen is much smaller than B&S and will have a ventilation duct at its base. It will hopefully hinge like a motorcycle visor to give forward. It is a wrap around screen so it will be easy to fit solar film to keep the heat out.

AERODYNAMICS
The basic aerodynamic shape of Quattro is a lot more complicated than B&S or a faired bike. The wheel spats, proximity to the ground and head fairing make it very difficult to imagine what is going on.

Graham Sparey-Taylor has been a great help in getting me started with CFD. He analysed my original model and pointed me in the right direction regarding tweaking the shape.

 
As can be seen from the initial CFD images, there is a lot going on, particularly around the wheel spats. The result of all this churning is an estimated aerodynamic drag of 18N at 35mph (15.5m/s) which equates to 290w. If the rolling resistance power of about 92W is added, you can see that an old git like me is going to struggle against another old git like Slash in the Beano. More work is needed!.........